Device including a conductive layer protected against oxidation

ABSTRACT

In a semiconductor device including a first conductive layer, the first conductive layer is treated with a nitrogen/hydrogen plasma before an additional layer is deposited thereover. The treatment stuffs the surface with nitrogen, thereby preventing oxygen from being adsorbed onto the surface of the first conductive layer. In one embodiment, a second conductive layer is deposited onto the first conductive layer, and the plasma treatment lessens if not eliminates an oxide formed between the two layers as a result of subsequent thermal treatments. In another embodiment, a dielectric layer is deposited onto the first conductive layer, and the plasma treatment lessens if not eliminates the ability of the first conductive layer to incorporate oxygen from the dielectric.

TECHNICAL FIELD

The present invention relates generally to a method of protectingagainst a conductive layer incorporating oxygen and a device includingthat layer. More specifically, the present invention relates to an insitu treatment of tungsten nitride.

BACKGROUND OF THE INVENTION

There is a constant need in the semiconductor industry to increase thenumber of dies that can be produced per silicon wafer. This need, inturn, encourages the formation of smaller die. Accordingly, it would bebeneficial to be able to form smaller structures and devices on each diewithout losing performance. For example, as capacitors are designed totake an ever decreasing amount of die space, those skilled in therelevant art have sought new materials with which to maintain or evenincrease capacitance despite the smaller size.

One such material is tantalum pentoxide (Ta₂O₅), which can be used asthe dielectric in the capacitor. Oftentimes, an electrically conductivelayer, such as one made of hemispherical silicon grain (HSG), underliesthe tantalum pentoxide and serves as the capacitor's bottom conductiveplate. With other dielectrics, it is preferable to have a layer ofpolycrystalline silicon (polysilicon) deposited over the dielectric toserve as the capacitor's top conductive plate. If polysilicon isdeposited directly onto tantalum pentoxide, however, several problemswill occur. First, silicon may diffuse into the tantalum pentoxide, thusdegrading it. Second, oxygen will migrate from the tantalum pentoxide,resulting in a capacitor that leaks charge too easily. Further, theoxygen migrates to the polysilicon, creating a layer of non-conductiveoxide, which decreases the capacitance. This can also be a problem whenusing barium strontium titanate ((Ba, Sr)TiO₃, or BST) as thedielectric.

In order to avoid these problems, it is known to deposit a top platecomprising two conductive layers. Polysilicon serves as the upper layerof the plate, with a non-polysilicon conductive material interfacingbetween the tantalum pentoxide and polysilicon. One such material oftenused is tungsten nitride (WN_(X), wherein X is a number greater thanzero). However, other problems arise with this process. Specifically, bythe end of the capacitor formation process, a layer of non-conductiveoxide often forms between the two conductive layers of the top plate.For ease of explanation, this non-conductive oxide will be assumed to besilicon dioxide (SiO₂), although other non-conductive oxides, eitheralone or in combination, may be present.

Without limiting the current invention, it is theorized that thetungsten nitride is exposed to an ambient containing oxygen. Thetungsten nitride adsorbs this oxygen due to bonds located on the grainboundaries of the tungsten nitride surface. Once the polysilicon layeris deposited, the device is then exposed to a thermal process. Forexample, the capacitor may be blanketed with an insulator, such asborophosphosilicate glass (BPSG). The BPSG layer may not be planar,especially if it is used to fill a trench in which the capacitor isconstructed. Heat is applied to the die to cause the BPSG to reflow andthereby planarize. The heat can cause the oxygen at the tungsten nitridesurface to diffuse into the polysilicon, wherein the oxygen and siliconreact to form silicon dioxide.

Regardless of the exact manner in which the silicon dioxide layer isformed, the result is that the HSG/Ta₂O₅/WN_(X)/SiO₂/polysilicon layersform a pair of capacitors coupled in series, wherein theHSG/Ta₂O₅/WN_(X) layers serve as one capacitor and theWN_(X)/SiO₂/polysilicon layers serve as the second capacitor in theseries. This pair of capacitors has less capacitance combined than thesingle HSG/Ta₂O₅/WN_(X)/polysilicon capacitor that was intended to beformed.

Other problems can occur with the association of WN_(X) and Ta₂O₅. Forexample, it is possible for the WN_(X) to serve as the bottom plate of acapacitor, underlying the Ta₂O₅ dielectric. In that case, the depositionof the Ta₂O₅ or a subsequent reoxidation of that layer may cause theWN_(X) layer to incorporate oxygen, thereby reducing capacitance.

It should be further noted that capacitor formation is not the onlycircumstance in which such problems can occur. There are many situationsin which an in-process multi-layer conductive structure is exposed tooxygen and is subjected to conditions that encourage oxidation. Anotherexample can be seen in the formation of metal lines. A layer of tungstennitride, or perhaps tantalum nitride, may serve as an interface betweenthe conductive material of a via and the metal line. If the interface isexposed to an ambient containing oxygen, then a thermal processinvolving the alloying or flowing of the metal in the metal line couldcause a similar problem with oxidation, thereby hindering electricalcontact.

As a result, there is a specific need in the art to prevent or at leastdecrease the degradation of capacitance in capacitors and of electricalcommunication in metal lines. There is also a more general need toprevent or at least protect against or minimize the migration of oxygenin relation to a conductive layer of a semiconductor device.

SUMMARY OF THE INVENTION

Accordingly, the current invention provides a method for protecting aconductive layer from oxygen. At least one exemplary embodiment concernspreventing or at least limiting a first conductive layer fromincorporating oxygen beneath the layer's surface. Other exemplaryembodiments address methods of limiting the first conductive layer'sability to adsorb oxygen. In doing so, such embodiments can help preventthe diffusion of oxygen into a second conductive layer, therebyprotecting against oxidation between conductive layers. One such methodserving as an exemplary embodiment involves exposing one of theconductive layers to an N₂/H₂ plasma before another conductive layer isprovided thereon. In a preferred embodiment, this step is performed insitu relative to the environment or ambient atmosphere in which the oneconductive layer was provided.

Other exemplary embodiments include the use of other nitrogen-containingplasmas, as well as the use of nitrogen-containing gases that are not inplasma form. Still other exemplary embodiments use gases that do notcontain nitrogen.

Further, alternate embodiments protect against oxidation betweenconductive layers with a step performed ex situ relative to theenvironment or ambient atmosphere in which the one conductive layer wasprovided. In one specific exemplary embodiment of this type, silane gasis flowed over the one conductive layer.

In preferred exemplary embodiments, at least one of the processesdescribed above is performed on a conductive material that has theability to adsorb or otherwise associate with oxygen. In a more specificembodiment, this material is a non-polysilicon material. Still morespecific exemplary embodiments perform one of the processes on tungstennitride or on tantalum nitride. In an even more specific exemplaryembodiment, a tungsten nitride layer is treated before providing apolysilicon layer thereover.

In yet another exemplary embodiment, a treatment such as the onesdescribed above occurs in the context of capacitor formation and, morespecifically, occurs in between depositing two conductive layers servingas the capacitor's top plate. In another exemplary embodiment, thetreatment occurs between depositing the bottom plate and the dielectricof a capacitor. In yet another exemplary embodiment involves treating aconductive layer as part of the formation of a conductive line.

In preferred embodiments, the method completely prevents the formationof the oxidation layer, although other exemplary embodiments allow forthe restriction of the oxidation layer. In some embodiments, thisoxidation layer is less than 10 angstroms thick. These methods alsoapply to embodiments concerning limiting a first conductive layer fromincorporating oxygen beneath the layer's surface. In addition, thecurrent invention also includes apparatus embodiments exhibiting thesecharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an in-process device as known in the prior art.

FIG. 2 depicts an in-process device having undergone an additional stepknown in the prior art.

FIG. 3 depicts an in-process device having undergone yet more stepsknown in the prior art.

FIG. 4 depicts one exemplary embodiment of the current invention.

FIG. 5 depicts a second exemplary embodiment of the current invention.

FIG. 6 depicts an in-process device as known in the prior art.

FIG. 7 depicts another in-process device as known in the prior art.

FIG. 8 depicts the in-process device in FIG. 7 having undergone anadditional step known in the prior art.

FIG. 9 depicts a third exemplary embodiment of the current invention.

FIG. 10 depicts a fourth exemplary embodiment of the current invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 depicts an “in-process” device 20—one that is in the process ofbeing constructed—having undergone processes known in the art. First, asubstrate 22 has been provided. In the current application, the term“substrate” or “semiconductor substrate” will be understood to mean anyconstruction comprising semiconductor material, including but notlimited to bulk semiconductive materials such as a semiconductor wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). Further, the term “substrate” also refers to anysupporting structure including, but not limited to, the semiconductivesubstrates described above. Over the substrate 22, a first conductivelayer 24 is provided. It is assumed for purposes of explanation onlythat the in-process device is a capacitor in the process of being built.Accordingly, the first conductive layer 24 serves as one of thecapacitor's conductive plates 25 (see FIG. 2) and may be made of HSG.Returning to FIG. 1, a dielectric 26 is provided which, in this case, istantalum pentoxide. Subsequently, a second conductive layer is provided,which is intended to serve as part of the other conductive plate for thecapacitor. Because the dielectric 26 is tantalum pentoxide, the secondconductive layer should not be polysilicon. Rather, in this case, thesecond conductive layer is assumed to be a tungsten nitride layer 28.Once the tungsten nitride layer 28 is provided, however, there may be atendency for oxygen to be adsorbed onto the surface of that layer 28.

Further, this adsorption may occur before a third conductive layer isprovided. This layer can be a polysilicon layer 30 illustrated in FIG.2. Ideally, the tungsten nitride layer 28 and the polysilicon layer 30define the other conductive plate 32.

However, if the third conductive layer is oxidizable, then furtherprocess steps may cause other results. For example, as seen in FIG. 3, asubsequent thermal process may cause a reaction between the polysiliconlayer 30 and the oxygen that had been adsorbed onto the surface of thetungsten nitride layer 28. In building a capacitor, this thermal processcan be the reflowing of a BPSG layer 34 that is deposited over thepolysilicon layer 30. The heat may cause the formation of a silicondioxide layer 36 between the tungsten nitride layer 28 and thepolysilicon layer 30, essentially creating two capacitors 38 and 40connected in series and having less combined capacitance than the onecapacitor originally intended.

One preferred exemplary embodiment of the current invention is a methodfor protecting against the formation of the silicon dioxide layer 36during the formation of the capacitor. Once the prior art steps depictedin FIG. 1 are carried out, this exemplary embodiment has the tungstennitride layer 28 exposed in situ to an N₂ and H₂ plasma. The term insitu indicates that the plasma process takes place in the same chamber,or at least within the same general atmosphere, as the process used toprovide the tungsten nitride layer. At the very least, the term in situindicates that the plasma process takes place before exposing thein-process device 20 to the atmosphere associated with providing thepolysilicon layer 30. Exemplary process parameters include a temperatureranging from about 150 to about 600 degrees Celsius; gas flows includingH₂ at about 50 to about 2000 sccm, N₂ at about 5 to about 1000 sccm, andAr at about 200 to about 2000 sccm; a radio frequency (RF) power rangingfrom about 50 to about 1000 W; a pressure ranging from about 1 millitorrto about 10 torr; and a process time ranging from about 10 seconds toabout 240 seconds. One of ordinary skill in the art, however, canappreciate that these parameters can be altered to achieve the same or asimilar process.

Without limiting the current invention, it is theorized that thistreatment stuffs the tungsten nitride grain boundaries with nitrogen orotherwise passivates the layer, thereby making the bonds at the grainboundaries less active. As a result, oxygen will be less likely to beadsorbed or otherwise become associated with the tungsten nitride layer,if at all. For example, without this treatment, a silicon dioxide layer36 about 10 to 40 angstroms thick will form between the tungsten nitridelayer 28 and the polysilicon layer 30 (see FIG. 3). The exemplaryprocess described above can result in a silicon dioxide layer 36 that isless than 10 angstroms thick, as seen in FIG. 4, and is preferablynon-existent, as illustrated in FIG. 5.

Moreover, the current invention is not limited to the process describedabove. There are other methods of providing nitrogen to the tungstennitride that are within the scope of this invention. For example,another such plasma treatment involves the use of ammonia (NH₃) in placeof the nitrogen and hydrogen. In using ammonia for the plasma,parameters such as the ones previously described can be used, exceptthat it is preferred to have a flow rate of ammonia ranging from about 5sccm to about 1000 sccm and a process time of up to 500 seconds. Yetanother embodiment includes a plasma treatment using N₂ without H₂. Inthat case, the exemplary process parameters are generally the same asthose used with N₂/H₂ plasma except that the flow rate of N₂ is 50-2000sccm.

Alternatively, ultraviolet light could be provided in place of RFenergy. For example, in using N₂ and H₂ or in using NH₃, the processparameters would be similar to the ones described above for those gases,except the RF energy would be replaced with UV light at a power rangingfrom 50 W to 3 kW.

Further, the current invention also includes within its scope othermethods of providing nitrogen without using electromagnetic energy toaffect the gas. One such exemplary embodiment still involves introducingammonia gas into the process chamber at the same flow rate and time asmentioned in the previous ammonia example, but at a pressure rangingfrom about 50 millitorr to about 1 atmosphere (760 torr).

In addition, the current invention is not limited to providing nitrogento the tungsten nitride. Other gases may provide a reducer, passivatormaterial, or some non-oxygen stuffing agent to the tungsten nitridesurface; or otherwise cause the tungsten nitride to associate with anoxygen-free material. A plasma treatment using H₂ without N₂ serves asone such embodiment. Exemplary parameters include a temperature rangingfrom about 150 to about 600 degrees Celsius; gas flows including H₂ atabout 50 to about 2000 sccm, and Ar at about 200 to about 2000 sccm; anRF power ranging from about 50 to about 1000 W; a pressure ranging fromabout 1 millitorr to about 10 torr; and a process time ranging fromabout 10 seconds to about 240 seconds.

Still other gases include diborane (B₂H₆); phosphine (PH₃); andcarbon-silicon compounds such as methylsilane (CH₃SiH₃) andhexamethyldisilane (CH₃)₃Si—Si(CH₃) ₃; and hexamethyldisilazane (HMDS).Additional alternate embodiments of the current invention use hydrazine(N₂H₄), monomethylhydrazine, carbon tetrafluoride (CF₄), CHF₃, HCl, andboron trichloride (BCl₃), which are also useful in passivatingdielectrics, as addressed in copending application Ser. No. 09/114,847.Also included are mixtures of any of the gases or types of gasesdescribed above. Exemplary non-plasma process parameters using theseother gases include a flow rate of about 2 sccm to about 400 sccm forthese gases; a flow rate of about 50 sccm to about 100 sccm for an inertcarrier gas such as He or Ar; a temperature ranging from about 150 toabout 600 degrees Celsius, a pressure ranging from about 50 millitorr toabout 1 atmosphere (760 torr); and a process time ranging from about 50to about 500 seconds. Again, one skilled in the art is aware that theseparameters can be altered to achieve the same or a similar process.

It is preferred that at least one of the processes described above occurbetween providing the tungsten nitride layer 28 and providing thepolysilicon layer 30. It is more preferable that one of the inventiveprocesses be carried out in a reducing atmosphere or at least before thetungsten nitride layer 28 is exposed to oxygen. Though such exposure isundesirable in many circumstances, it may be unavoidable. For example,the tungsten nitride layer 28 may be exposed to the cleanroom air atsome point during processing. Thus, it is even more preferable to treatthe tungsten nitride layer 28 in situ relative to the environment orambient atmosphere used to provide the tungsten nitride layer 28. It isstill more preferable to cover the treated tungsten nitride layer 28before the in-process device 20 is exposed, even unintentionally, tooxygen. This is preferable because any exposure may allow at least someoxygen to associate with the tungsten nitride layer 28, even after oneof the inventive treatments disclosed herein. Nevertheless, it is notnecessary under the current invention to discourage oxygen adsorptionbefore exposing the in-process device to the atmosphere associated withproviding the polysilicon layer 30. If the in-process capacitor 20 isremoved from the environment used to provide the tungsten nitride layer28 and one of the inventive processes described has not been performed,then another option within the scope of the current invention is toexpose the tungsten nitride layer 28 to a reducing atmosphere beforeproviding the polysilicon layer 30. This can be done by flowing silanegas (SiH₄) into the environment of the in-process device 20. Processparameters include a silane flow ranging from 50 to 1,000 sccm, apressure of 10 torr to 1 atmosphere, a temperature ranging from 300 to700 degrees Celsius, and a process time ranging from 10 to 300 seconds.Moreover, this silane treatment, if chosen, is not limited to ex situsituations. Silane gas may be used in place of or in combination withthe in situ treatments described herein. Accordingly, any combination ofthe individual processes covered by the current invention are alsowithin its scope.

As mentioned in the background section, oxygen diffusing away from thetungsten nitride is not the only concern when using that layer alongwith tantalum pentoxide. As seen in FIG. 6, a tungsten nitride layer 128is deposited over the substrate 122. A dielectric layer 126, assumed tobe tantalum pentoxide, is deposited over the tungsten nitride layer 128.Assuming the in-process device of FIG. 6 represents the early stage of acapacitor, the tungsten nitride layer 128 will serve as the bottom platerather than part of the top plate as depicted in previous figures. Theprocess of depositing the tantalum pentoxide dielectric layer 126 maycause the tungsten nitride layer 128 to incorporate oxygen. In addition,further processing, such as a reoxidation of the tantalum pentoxidedielectric layer 126 may cause the tungsten nitride layer 128 toincorporate still more oxygen. This incorporation of oxygen will reducethe capacitance of the finished device. Under these circumstances, apreferred embodiment of the current invention calls for exposing thetungsten nitride layer 128 to an N₂/H₂ plasma before depositing tantalumpentoxide dielectric layer 126. This plasma is created under theparameters already disclosed above. Although using an N₂ and H₂ plasmais preferred, the alternatives presented earlier—such as a non-plasmaprocess, the use of another nitrogen-containing gas, or the use of anitrogen-free gas, may also be used under these circumstances, and suchalternatives fall within the scope of the invention. Further, it is notrequired to use tungsten nitride and tantalum pentoxide as the twolayers, as embodiments of the current invention will work on otherconductive layers and dielectric layers as well.

Thus, embodiments of the current invention protect against a conductivelayer associating with oxygen in at least two circumstances. First,where a dielectric is deposited over a conductive layer, the disclosedmethods help prevent oxygen from being incorporated within theconductive layer. Second, when a second conductive layer is depositedover the initial conductive layer, the disclosed methods inhibit oxygenfrom being incorporated by the second conductive layer and forming anoxide.

It should be further noted that embodiments of the current invention arenot limited to the circumstances related to the formation of capacitors.As further mentioned in the background section, a similar risk ofoxidation between two conductive materials can occur during theformation of metal lines in a semiconductor device. As seen in FIG. 7,insulation 42 has been deposited over the substrate 22 and subsequentlyetched to define a via 44. The via is filled with a conductive material,such as polysilicon, tungsten, copper, or aluminum. In thisconfiguration, the conductive material may be referred to as a “plug”46. The plug 46 will allow electrical communication between theunderlying substrate 22, which may be doped to serve as part of atransistor, and the overlying line material 48. The line material 48 maybe copper or some other conductive material, including an alloy. Theline material 48 is often deposited within a container 50, also definedby etching insulation 42. (One skilled in the art can appreciate thatdifferent layers of insulation may define the via 44 and the container50.)

As a part of this process, it may also be preferred to include aninterposing layer 52 between the line material 48 and the plug 46. Forpurposes of explaining the current invention, it is assumed that theinterposing layer 52 comprises tungsten nitride. This interposing layer52 may enhance electrical contact between the line material 48 and theplug 46, promote adhesion of the line material 48 within the container50, prevent or slow the diffusion of material across its boundaries, orserve some other purpose.

Regardless of the intended or inherent purpose, this interposing layermay adsorb oxygen after it is formed. Moreover, there may be thermalprocesses involved with or occurring subsequent to providing the linematerial 48. Such a thermal process could be used to deposit, flow, oralloy the line material 48. As a result of this or any other thermalprocess, it is believed that the oxygen adsorbed by the tungsten nitrideinterposing layer 52 will react with the line material 48, therebyforming an oxide layer 54 between the interposing layer 52 and the linematerial 48 (FIG. 8). This oxide layer 54, being an insulator, willhinder the ability to allow electrical communication between the linematerial 48 and the plug 46. Accordingly, the exemplary methodsdescribed above may be used to reduce the oxide layer 54 to a thicknessof less than 10 angstroms and preferably down to 0 angstroms, as seenrespectively in FIGS. 9 and 10.

One skilled in the art can appreciate that, although specificembodiments of this invention have been described for purposes ofillustration, various modifications can be made without departing fromthe spirit and scope of the invention. For example, it is not necessaryto use an exemplary treatment of the current invention on a tungstennitride layer. The invention's embodiments will also be effective ontantalum nitride surfaces, as well as other surfaces that may adsorb orotherwise associate or interact with oxygen.

Further, it should also be noted that the general process describedabove for providing a metal line could be considered a damasceneprocess, wherein a hole in insulation is filled with metal. This type ofprocess is contrasted to processes wherein a continuous layer of metalis etched to a desired configuration and then surrounded withinsulation. More specifically, the metal line process describe above isan example of a dual damascene process. It follows, then, that thecurrent invention may be applied in any type of damascene process.Moreover, one skilled in the art will now be able to appreciate thatthat exemplary methods embodying the current invention apply to anysituation involving the prevention, minimization, or change in a factoraffecting the association of oxygen with a conductive layer. As aresult, the current invention also includes within its scope devicesthat comprise two conductive layers and a minimal amount of oxide, ifany, therebetween. Accordingly, the invention is not limited except asstated in the claims.

What is claimed is:
 1. A capacitor, comprising: a first plate; adielectric over said first plate, wherein said dielectric containsoxygen; a second plate over said dielectric, comprising: a firstnon-polysilicon conductive layer over said dielectric, wherein saidfirst non-polysilicon conductive layer contains nitrogen; and a secondconductive layer over said first non-polysilicon conductive layer,wherein said second conductive layer comprises polysilicon.
 2. Thecapacitor in claim 1, wherein: said dielectric layer consists of aselection from tantalum pentoxide and barium strontium titanate; andsaid first non-polysilicon conductive layer consists of a selection fromtungsten nitride and tantalum nitride.
 3. The capacitor in claim 2,wherein said second plate comprises an oxygen-free second plate.
 4. Thecapacitor in claim 2, wherein said second plate comprises an oxide layerbetween said first non-polysilicon conductive layer and said secondconductive layer, wherein said oxide layer is less than 10 angstromsthick.
 5. The capacitor in claim 2, wherein said first non-polysiliconconductive layer and said second conductive layer are less than 10angstroms apart and are separated by a silicon dioxide layer.
 6. A pairof series-coupled capacitors, comprising: a first conductive layer; adielectric over said first conductive layer; a second conductive layerover said dielectric; a third conductive layer less than 10 angstromsover said second conductive layer; and an oxide of said third conductivelayer between said second conductive layer and said third conductivelayer.
 7. The pair of series-coupled capacitors in claim 6, wherein saidfirst conductive layer, said dielectric, and said second conductivelayer define a first capacitor; and wherein said second conductivelayer, said oxide, and said third conductive layer define a secondcapacitor.